Dislocation accumulation in gallium-arsenide film, which is deposited on silicon substrate and cooled down from the deposition to room temperature, is examined by crystal plasticity simulation. A new approach to suppression of dislocation accumulation is proposed such that selective growth of the film and partial doping of impurities into it are combined. The results show the possibility to localize the plastic deformation near the film/substrate interface and to keep the surface region of the film almost dislocation-free. Geometry of the selectively grown film and a strategy for partial doping of impurities, which suppresses the dislocation accumulation in the surface region of the film, are considered.

We have observed the complete delamination of polycrystalline chromium films from single crystal silicon substrates during deposition due to the formation of high internal stresses. These intrinsic stresses can give rise to interfacial defects which assist in the separation of the film from the substrate. Stresses in the film are balanced by stresses in the substrate, which cause mechanical failure in the substrate near the interface. Extensive arrays of dislocations and cracking of the substrate have been observed. We find that the delamination of the films from the substrate is initiated by the formation of damage in the substrate, rather than to the film or the interface.

Tungsten-carbon coatings have been deposited on stainless steel substrates by reactive magnetron sputtering from Ar–CH4 mixtures. The carbon concentration in the coatings measured by electron microprobe analyses was found to be proportional to the CH4 flow rate. Only the cubic α–W phase with a dilated lattice parameter was identified in W–C coatings having a carbon content lower than 25 at. %. Since the lattice parameter of the α–W phase in these W–C coatings increased with increasing carbon content, these coatings may be assumed to be W–C solid solutions. Only the nonstoichiometric β–WC1−x carbide (cubic phase) was detected in W–C coatings containing 30 to 70 at. % of carbon. The chemical state of the elements was investigated by x-ray photoelectron spectroscopy. The Vickers hardness of the W–C coatings was found to be considerably dependent on the carbon concentration. A maximum microhardness of 26 000 MPa was measured for W–C coatings containing either 14–15 at. % or 40–45 at. % of carbon. The correlation between crystallographic structure and microhardness is analyzed and discussed in this paper.

We have observed the formation of the hydrotalcite-like phase of lithium dialuminate, LiAl2(OH)6OH · 2H2O, and also the carbonate analog, by the oxidation of aluminum sheet and also aluminum powder in aqueous lithium hydroxide or lithium carbonate solutions. A secondary phase, bayerite, was also observed following the oxidation process, except when the aluminum was treated with lithium oxalate solutions where it is the principal phase. Results have been obtained for the time required to form a passivating film to hydrogen formation as a function of temperature and oxidizing solution. Grazing incidence x-ray diffraction of aluminum sheet samples, combined with polycrystalline x-ray diffraction on similarly treated aluminum powder, were used to evaluate the formation of the films. Both transmission and reflectance infrared absorption spectra on powder and sheet samples were used to support the x-ray observations. Scanning and transmission electron microscopies show morphological differences between preparations, film thicknesses of 10–20 μm, and also film defects. Additional SIMS analysis determined the relative lithium and aluminum concentrations in the films, suggesting that a higher concentration of lithium occurs when lithium carbonate is present in the reacting solutions.

We present the results of a combined experimental and theoretical investigation of phase separation and microstructure development in co-deposited Al–Ge thin films. For small film thicknesses and deposition temperatures above 150 °C the phase-separated films consist of an array of domains of the Al- and Ge-rich terminal phases (lateral phase separation). Films deposited at 100 °C or less contained one or both of the terminal phases plus a metastable phase. We show that the domain structure evolves during deposition in a manner consistent with a surface interdiffusion controlled process. As film thickness increases we observe a transition from the laterally phase-separated microstructure to a layered microstructure exhibiting phase separation perpendicular to the film/substrate interface (transverse phase separation), with Al segregating to the film surface. We present a thermodynamic argument based on the competition between surface and interfacial free energies to explain this transition. Finally, we discuss the stability of the transverse phase-separated microstructure in the thick-film limit in terms of the transport of Ge through the Al-rich surface layer.

The fracture strength of polycrystalline diamond films deposited by filament assisted chemical vapor deposition in the thickness range of 3.5 to 160 μm is investigated. Using a burst pressure technique, the fracture strengths of circular diamond film specimens are calculated. An average fracture strength of 730 MPa for nine samples was computed. This value is in good agreement with published strengths of microwave plasma deposited diamond films, comparable to other high strength materials, and within an order of magnitude of the fracture strength of bulk natural diamond. The average fracture strength of the fine-grained substrate interface appears consistently higher than that of the coarse-grained diamond growth surface.

Material properties are greatly dependent upon the structure of the material. This paper, the first of three parts, discusses how composition influences the crystallographic structure and microstructure of lead lanthanum titanate (PLT) thin films grown by the multi-ion-beam reactive sputtering (MIBERS) technique. A transmission electron microscopy (TEM) study detailing the relationship between crystallographic texturing and microstructure development will be presented in a second paper. The dependence of the ferroelectric properties on observed crystallographic structure and microstructure is presented in the third paper of this series. As-deposited PLT microstructures coincide with the structure zone model (SZM) which has been developed to describe the microstructure of thin films deposited by physical vapor deposition. The as-deposited PLT structures are altered during post-deposition annealing as a result of crystallization and PbO evaporation. Amorphous films with more than 10 mole % excess PbO become polycrystalline with porous microstructures after annealing. When there is less PbO in the as-deposited film, 〈100〉 texture and dense structures are observed. Porosity results from PbO evaporation, and 〈100〉 texture is inhibited by excess PbO.

Diamond thin films have been successfully grown on monocrystalline Si and various polycrystalline substrates, such as Mo, Nb, Zr, Cu, SiC, SiOx2, and WC, by microwave plasma CVD in gas mixtures of methane and hydrogen. For instance, high purity and dense diamond films can be deposited on structurally matched substrates of Si and SiC, in hydrogen containing 0.2% methane. SEM, TEM, XRD, AES, EELS, EDS, and Raman spectroscopy have been utilized to study and characterize the morphology, microstructure, and composition of the deposited films. Results indicate that tetrakaidecahedra are the dominant forms of crystalline diamond. Both {100} and {111} facets were observed on all substrates studied. SiC, SiOx, amorphous carbon, and carbides of refractory metals were the dominant interphases in this study. The composition and microstructure of the interphase appear to have significant effects on the adhesion strength, as shown in the diamond/Mo and diamond/Hf systems. Structural defects such as twins and stacking faults were frequently observed inside the diamond grains, while line defects of dislocations were mainly constrained to the grain boundaries. The diamond nucleation rate could be increased by first modifying the surface of the substrate material using a process that ultrasonically stimulated cavitation-erosion in an aqueous suspension of diamond dust. The diamond crystallites growing on this roughened surface were of a much more uniform size than was achieved after the more conventional lapping process.

We conducted a series of hydrostatic and constant shear stress experiments at room temperature on three different sintering runs of unpoled, niobium-doped lead-zirconate-titanate ceramic (PZT 95/5–2Nb) in order to quantify the influence of shear stress on the displacive (possibly martensitic), first-order, rhombohedral → orthorhombic phase transformation. Inter- and intra-batch variations were detected, but some generalizations can be made. In hydrostatic compression at room temperature, the transformation began at approximately 260 MPa, and was usually incompletely reversed upon return to ambient conditions. Strains associated with the transformation were isotropic, both on the first and subsequent hydrostatic cycles. Results for the constant shear stress tests were very different. First, the confining pressure and mean stress at which the transition begins decreased systematically with increasing shear stress. Second, we observed that the rate of transformation decreased with increasing shear stress and the associated elastic shear strain. This result contrasts with the typical observation that shear stresses increase reaction and transformation kinetics. Third, strain was not isotropic during the transformation: axial strains were greater and lateral strains smaller than for the hydrostatic case, though volumetric strain behavior was comparable for the two types of tests. However, this effect does not appear to be an example of transformational plasticity: no additional unexpected strains accumulated during subsequent cycles through the transition under deviatoric loading. If subsequent hydrostatic cycles were performed on samples previously subjected to shear stress, strain anisotropy was again observed, indicating that the earlier superimposed shear stress produced a permanent mechanical anisotropy in the material. The mechanical anisotropy probably resulted from a crystallographic preferred orientation that developed during the transformation under shear stress. Finally, in a few experiments on specimens from one particular sintering run, volume strain was often completely recovered and sporadic evidence for a shape memory effect was observed.

An experimental method to obtain the grain boundary geometry using the transmission electron microscope is presented. The method allows Σ determination including grain boundary plane orientation. In order to determine the specialness of the grain boundary, three different criteria for maximum allowable deviations from exact CSL misorientations were examined. We tested these three criteria from a statistical distribution of grain boundary types in terms of Σ. We compared grain boundary distributions from other studies in Ni3Al and found discrepancies among them. It seems that the discrepancy came from the different criteria for special boundaries in Σ determination and different experimental procedures they used. The statistical distribution of grain boundary plane orientations showed that low Σ boundaries (Σ < 11) were oriented to the plane of high density of coincident sites.

Nonequilibrium titanium-nitride alloy powders have been fabricated by a high energetic ball mill under nitrogen gas flow at room temperature and characterized by means of x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry. Initial hcp titanium is completely transformed to nonequilibrium-fcc Ti–N after 720 ks of the milling time. The fcc Ti–N phase is stable at relatively low temperature and transforms at 855 K to Ti2N and δ phases. At the final stage of milling, the particle- and grain-sizes of alloy powders are 1 mm and 5 nm, respectively, and the lattice parameter is 0.419 nm.

Structural and textural changes in carbon films prepared from the polyimide Kapton with heat-treatment temperatures up to 3000 °C were followed by measuring the magnetoresistance at 77 K, the ratio of electrical resistivity at room temperature to that at 77 K, and x-ray powder patterns. The maximum magnetoresistance (Δρ/ρ)max as a measure of graphitization changed its sign from negative to positive around 2500 °C and then increased its value abruptly. The resistivity ratio ρR.T./ρ77 K increased above 2500 °C treatment. The values of (Δρ/ρ)max and ρR.T./ρ77 K after 3000 °C treatment reached 275% and 0.93, respectively. The average interlayer spacing d002 after the 3000 °C treatment was 0.3354 nm, the same as natural graphite. The changes in structure and texture in the film were consistent with the model proposed in the previous paper from observation by transmission electron microscopy.

It is argued that interdiffusion must precede nucleation of new phases during reactions at interfaces between compositionally different phases. The relative rates at which elemental components diffuse in the reacting phases control the sequence in which phases can form, and can also strongly affect the relative nucleation rates of alloy products, especially in the transient nucleation regime. While detailed predictions of the relative nucleation rates require usually unavailable knowledge of the energies of the relevant interfaces, in some cases, knowledge of the relevant diffusivities, along with a thermodynamic analysis, can lead to predictions of likely phase formation sequences. These concepts are used to explain the association of diffusional asymmetry with systems that undergo solid state amorphization, and to specify semiquantitatively the degree of asymmetry required for solid state amorphization.

We have developed a two-step hot filament chemical vapor deposition method to form polycrystalline films of diamond on Hastelloy substrates. The first step at a lower temperature results in the deposition of a composite layer of carbon, diamond-like carbon, and diamond, which provide nucleation sites for diamond growth in the second step at a higher temperature. To obtain a cleaner amorphous carbon-free diamond film, we introduced an intermediate hydrogen etching step. Using this procedure, we have obtained high quality polycrystalline diamond film on Hastelloy substrates, as characterized by scanning electron microscopy and Raman measurements.

A model exploring the effect of the presence of a single hydrogen interstitial on the crack tip configuration of nickel is described. The model is based on a EAM-type potential developed by Daw, Baskes, Bisson, and Wolfer for describing the Ni–Ni, Ni–H, and H–H interactions, and involves the crack tip region of a semi-infinite crack in an infinite solid. Several types of interactions are observed to occur. In a model oriented such that dislocation emission is difficult, hydrogen is observed to increase the crack tip opening displacement (CTOD), exert a force on the crack tip due to interaction between the dilatancy of the defect and the hydrostatic component of the field of the crack, and increase the local tensile stresses. However, the largest contribution to extending the crack derives from the energy released when a hydrogen interstitial escapes to the crack surface. A hydrogen interstitial is also observed to assist dislocation emission in models with an easy emission orientation.

Finely dispersed metal powders have been obtained after chemical reduction of Ni and Co acetylacetonate by lithium aluminum hydride in tetrahydrofuran at low temperature. The Al/Ni and Al/Co stoichiometry of the as-reduced powders was 1.1 and 1.2, respectively. The structure and thermal stability of the as-reduced powders were affected by the temperature of reduction. For the NiAl powders it was found that the thermal treatment initially induces a separation of highly unstable Ni(Al) and Al(Ni) solid solutions, which subsequently react to give a single NiAl phase of cubic structure not reported in the equilibrium phase diagram. Conversely, the reduction of cobalt acetylacetonate directly gives a cubic metastable phase, from which precipitates some hexagonal form of Co after treatment at 450 °C.

Metal-containing amorphous hydrogenated carbon (Me–C: H) films were prepared on silicon substrates. Two kinds of metals (Ti, Ta) were incorporated in the process of reactive rf diode— (13.56 MHz) and DC-magnetron sputtering, respectively. Elastic recoil detection (ERD) and Rutherford backscattering (RBS) of MeV He+ ions were used to determine the hydrogen content and mass density of Me–C: H films. The mechanical properties, i.e., microhardness, Young's modulus, and adhesion, were measured with the help of a nanoindenter and scratch tester. Results show that (1) the mechanical properties of Me–C: H films depend mainly on metal concentrations. At a certain metal concentration, optimal hardness, Young's modulus, and critical load were obtained; (2) the M–C: H films with an optimal metal concentration possess similar hardness, Young's modulus, and higher critical load compared with the corresponding values of diamond-like carbon (a–C: H) films, due to the improvement of the toughness of the films by the incorporation of metals. Therefore, Me–C: H films show high promise of being wear-resistant protective coatings.

A series of molybdenum nitride films were synthesized by implanting energetic nitrogen ions into molybdenum thin films. The resulting films were characterized using x-ray diffraction to determine the effects of nitrogen ion dose (4 × 1016−4 × 1017 N+/cm2), accelerating voltage (50–200 kV), and target temperature (∼298–773 K) on their structural properties. The order of structural transformation with increased incorporation of nitrogen ions into the Mo film can be summarized as follows: Mo → γ−Mo2N → δ−MoN. Nitrogen incorporation was increased by either increasing the dose or decreasing the ion energy. At elevated target temperatures the metastable B1–MoN phase was also produced. In most cases the Mo nitride crystallites formed with the planes of highest atomic density parallel to the substrate surface. At high ion energies preferential orientation developed so that the more open crystallographic directions aligned with the ion beam direction. We tentatively attributed this behavior to ion channeling effects.

The relative stability of standard extended dislocation dipoles and some new stable defects with lozenge-shaped cross sections have been numerically estimated. An earlier study of these defects in an isotropic fee structure has been extended to the anisotropic case to assess the effect of anisotropy on the calculations. The study is further extended to the case of the L12 crystal structure of the ordered alloy Ni3Al, where the Burgers vectors are large. Results indicate that the introduction of anisotropy has a small effect in determining the relative stability of extended dislocation faults. The results also show that the large values of the Burgers vectors stabilize the arrays in Ni3Al and that the most stable defect favored is the screw lozenge array LD.

An experimental study of the effects of temperature and pressure on the conductivity anisotropy of aligned short carbon fiber filled epoxies is presented. The data give evidence of significant relative changes of the anisotropy whose sign and amplitude depend on the volume concentration near the conductivity threshold. A phenomenological approach involving variations with temperature and pressure of the fiber volume fraction and the fiber aspect ratio is developed. It predicts that the anisotropy change results from two competing contributions in a similar way whether the temperature or the pressure is varied. Although quantitative predictions cannot be made, we show that introducing the available mechanical and thermal materials constants into the theoretical equations accounts, at least qualitatively, for the experimental behaviors.